The present invention relates generally to digital film development systems, and more particularly to a digital film development system which includes a method and system for aligning multiple scans of the same area of film using film non-uniformity.
Color photographic film generally comprises three layers of light sensitive material that are separately sensitive to red, green, and blue light. During conventional color photographic film development, the exposed film is chemically processed to produce dyes in the three layers with color densities directly proportional to the blue, green and red spectral exposures that were recorded on the film in response to the light reflecting from the photographed scene. Yellow dye is produced in the top layer, magenta dye in the middle layer, and cyan dye in the bottom layer, the combination of the produced dyes revealing the latent image. Once the film is developed, a separate printing process can be used to record photographic prints, using the developed film and photographic paper.
In contrast to conventional film development, digital film development systems, or digital film processing systems, have been developed. One such process involves chemically developing exposed film to form scene images comprised of silver metal particles or grains in each of the red, green, and blue recording layers of the film. Then, while the film is developing, it is scanned using electromagnetic radiation, such as light with one predominant frequency, preferably in the infrared region. In particular, as the film develops in response to chemical developer, a light source is directed to the front of the film, and a light source is directed to the back of the film. Grains of elemental silver developing in the top layer (e.g., the blue sensitive layer) are visible from the front of the film by light reflected from the front source; however, these grains are hidden from the back of the film. Similarly, grains of elemental silver developing in the bottom layer (e.g., the red sensitive layer) are visible from the back of the film by light reflected from the back source; however these grains are hidden from the front. Meanwhile, grains of elemental silver in the middle layer (e.g., the green sensitive layer) are hidden from the light reflected from the front or back; however, these grains are visible by any light transmitted through the three layers, as are those grains in the other two layers. Thus, by sensing, for each pixel location, light reflected from the front of the film, light reflected from the back of the film, and light transmitted through the film, three measurements can be acquired for each pixel. The three measured numbers for each pixel can then be solved for the three colors to arrive at three color code values for each pixel, and the plurality of colored pixels can then be printed or displayed to view the image.
Such scanning of each image on the film can occur at multiple times during the development of the film. Accordingly, features of the image which may appear quickly during development can be recorded, as well as features of the image which may not appear until later in the film development. The multiple digital image files for each image which are created by the multiple scannings can then be combined to form a single enhanced image file, which captures features of the image which appear during various development stages of the film.
However, in order to combine the multiple digital image files of a particular film image or exposure, the pixel data arrays which make up these files must be properly aligned. Otherwise, if the pixel data from one digital image is skewed with respect to the pixel data from another digital image, the combined image will not very accurately represent the image which was developing on the film.
Utilizing film sprocket holes is one potential method to align multiple digital image files. In particular, if data from a first digital image can be identified as representing a sprocket hole on the film edge, and if the corresponding sprocket hole can be identified from a second digital image, then the two digital images could be aligned. Another potential method of alignment involves identifying data from the digital image files which represent the corner of the film exposure. In particular, if data from a first digital image can be identified as representing the corner of the film image or exposure, and if the corresponding corner can be identified from a second digital image, then the two digital images could be aligned.
However, such methods are not without disadvantages. In particular, identifying sprocket holes from a digital image file can be difficult. Because sprocket holes are three dimensional in nature, the edges of the hole can appear very fuzzy and not well-defined. Moreover, at high resolution, the sprocket holes appear very large in the digital image file, and so large portions of data must be processed for aligning such holes. Moreover, minor differences in illumination between the two scannings of the film can cause different shadows or highlights to appear between the two resulting digital image files, making the identification of two corresponding sprocket holes difficult. In addition, sprocket holes can be mangled during picture taking or film development, creating additional identification problems. Finally, if film is not kept taut during the multiple scannings, even if the sprocket holes can be aligned, the rest of the digital image files still might not be accurately aligned.
Locating comers of an exposure also can have disadvantages. In particular, not every exposure will have a well-defined comer. For example, an exposure that has dark surroundings, such as a picture of the moon at night for example, might not include an identifiable corner of the exposure frame. Moreover, early during the film development, comers of an exposure are typically not very well-defined. Thus, it can be difficult to identify a corner of an exposure from a digital image file that was created by scanning early during the development of the exposure.
Accordingly, there remains a need for a more accurate method and apparatus for more accurately and easily aligning multiple scans of the same portion of a medium. In particular, there remains a need for such a method and apparatus which can be used to align multiple digital image files which were created by scanning the same film exposure during multiple film development stages of the exposure.
According to one embodiment of the invention, a method is provided for aligning two or more digital images created by scanning the same portion of a medium. The method comprises obtaining a first digital image and obtaining a second digital image. A target portion is selected from the first digital image, and a first portion is selected from the second digital image. A first mathematical correlation between the target portion and the first portion is calculated. One or more additional portions of the second digital image are selected, and mathematical correlations between the target portion and these additional portions are calculated. An alignment offset between the two images is determined using the mathematical correlations. For instance, a curve can be fit through the highest correlation and each of its neighboring correlations, and the vertex of the curve can be used for the alignment offset. Once aligned, the images can be combined to create a single digital image.
It is an advantage of at least one exemplary embodiment of the present invention to accurately align two or more digital images.
An advantage of at least one exemplary embodiment of the present invention is to align digital images without reliance on features of the scene which the digital image represents.
It is an advantage of one or more exemplary embodiments of the invention to align digital images scanned from the same frame of film, without reliance on film sprocket holes or the scene exposed on the film.
Still other advantages of various embodiments will become apparent to those skilled in this art from the following description wherein there is shown and described exemplary embodiments of this invention simply for the purposes of illustration. As will be realized, the invention is capable of other different aspects and embodiments without departing from the scope of the invention. Accordingly, the advantages, drawings, and descriptions are illustrative in nature and not restrictive in nature.